Most electronic instruments generate musical tones that have a constant spectral output. In contrast, most conventional musical instruments produce tones in which the spectral output varies with time. It is these changes in harmonic content of the tone being generated by a musical instrument which to a large measure gives the "natural" musical sound characteristic of the particular instrument. It is this lack of such time variations in the spectral content of the tone being generated that gives electronic musical instruments their "artificial" sound quality. To overcome this constant tone and to add interest and a more natural quality to the tone generated, various attempts have been made in electronic musical instruments to vary the harmonic content of the tone being generated by passing the musical waveshape through filters whose cutoff frequencies are caused to vary in a predetermined time variant manner. Filters of this type are referred to as formant filters. Copending application Ser. No. 857,436, filed Dec. 5, 1977, entitled "Resonator For a Musical Tone Synthesizer", now U.S. Pat. No. 4,175,463, by the same inventor as the present application, shows one such arrangement for producing a time variant effect. In copending application Ser. No. 866,336 filed Jan. 3, 1974, entitled "A Musical Generator With Time Variant Overtones", now U.S. Pat. No. 4,175,464, by the same inventor as the present application, frequency modulation of a carrier by modulating signals of equal or integral multiples of the carrier frequency is described. In U.S. Pat. No. 4,085,644 there is disclosed a polyphonic tone synthesizer in which a formant filter effect is implemented by varying the harmonic coefficients that are used in computing musical waveshapes from tables of harmonic coefficients.